Conventionally, an anisotropic conductive adhesive in which conductive particles are dispersed within an adhesive material has been widely used in coupling or assembling semiconductor devices, wiring boards, or the like.
Situations where two wiring boards are coupled in using the anisotropic conductive adhesive of the conventional art will be explained. FIG. 1(a) is an illustration of a process for coupling a wiring board 110 and a wiring board 120 to each other by means of the anisotropic conductive adhesive with use of the conductive particles, showing as a state prior to pressuring with heating. After rendering a metallic wiring 115 of the wiring board 110 and a metallic wiring 125 of the wiring board 120 face to each other, an anisotropic conductive adhesive 130 is sandwiched between surfaces of the wiring board 110, 120, having the metallic wiring 115,125, respectively.
Upon heating to press the entire portions in the above condition, an adhesive material 138 in the anisotropic conductive 130 is softened by heating, while by pressing, the metallic wirings 115, 125 push away the softened adhesive material 138, so that conductive particles 135 dispersed within the adhesive material 138 are sandwiched between the metallic wirings 115,125.
Where heating is further continued, the adhesive material 138 is hardened in a state while the conductive particles 135 are sandwiched between the metallic wirings 115, 125, and therefore, an electric device 101 as shown in FIG. 1(b) can be obtained. In the electric device 101, the two wiring boards 110 120 are coupled to each other not only mechanically by the hardened adhesive material 139 but also electrically through the conductive particles 135.
Meanwhile, it has been known that in using conductive particles having high compression deformation ratio as the conductive particles 135, the conduction reliability is improved since a process of heating with pressure compresses and deforms the conductive particles to enlarge the contact area between the conductive particles and the metallic wirings.
Publicly known as such a particle is a conductive particle in which a conductive coating is formed on a surface of a core particle comprised of a resin particle (see, e.g., Japanese Patent Application Publication No. JA-11-73817). The resin particle used for the core particle is formed by a condensation method for condensing resin particles having a small size or sizes, or y a seed polymerization method for growing seed particles by emulsion polymerization, so that such a resin particle has the high compression deformation ratio, thereby increasing the compression deformation ratio of the conductive particles, as a whole.
Even such a conductive particle, however, does not have the sufficient compression deformation ratio, and the conductive particles may be broken down when the pressing load is made larger to increase the deformation amount.